1. Field of the Invention
This invention relates generally to the field of plastic containers, and more particularly to plastic containers that are designed to accommodate volumetric expansion and contraction such as that inherent to the hot-fill packaging process or to packaging applications where internal pressurization is anticipated.
2. Description of the Related Technology
Many products that were previously packaged using glass containers are now being supplied in plastic containers, such as containers that are fabricated from polyesters such as polyethylene terephthalate (PET).
PET containers are typically manufactured using the stretch blow molding process. This involves the use of a preform that is injection molded into a shape that facilitates distribution of the plastic material within the preform into the desired final shape of the container. The preform is first heated and then is longitudinally stretched and subsequently inflated within a mold cavity so that it assumes the desired final shape of the container. As the preform is inflated, it takes on the shape of the mold cavity. The polymer solidifies upon contacting the cooler surface of the mold, and the finished hollow container is subsequently ejected from the mold.
Hot fill containers are designed to be used with the conventional hot fill process in which a liquid or semi-solid product such as fruit juice, sauce, salsa, jelly or fruit salad is introduced into the container while warm or hot, as appropriate, for sanitary packaging of the product. After filling, such containers undergo significant volumetric shrinkage as a result of the cooling of the product within the sealed container. Hot fill type containers accordingly must be designed to have the capability of accommodating such shrinkage. Typically this has been done by incorporating one or more vacuum panels into the side wall of the container that are designed to flex inwardly as the volume of the product within the container decreases as a result of cooling.
Typically, the vacuum panel regions of conventional hot fill containers are characterized by having surfaces that are designed to deflect inwardly when the product within the sealed container undergoes shrinkage. The amount of volumetric contraction, also referred to as vacuum uptake, that can be provided by a conventional vacuum panel is limited by the size of the panel. The design of such containers is often influenced by the aesthetic preferences of manufacturers, which in some instances can limit the size of the vacuum panels to the extent that makes it difficult or impossible to achieve the necessary vacuum uptake capacity.
In certain types of hot-fill containers, the flexible vacuum panels are disposed about the entire circumference of the container sidewall, separated from each other by a corresponding number of posts that are interposed between the vacuum panels. One problem that has afflicted many conventional hot-fill container designs of this type is uneven or asymmetric deflection of the different vacuum panels under vacuum uptake conditions. The possibility of such inconsistent deformation makes it difficult to reliably design a container having the desired amount of vacuum uptake capability, and it is also unsightly.
A need therefore exists for an improved vacuum panel configuration that achieves a maximal amount of reliability in terms of vacuum panel deflection under vacuum uptake conditions.